The invention relates to a process for the removal of hydrogen sulphide and other sour gas components from industrial gases under pressure by means of physical scrubbing agents, to the recovery of sulphur from hydrogen sulphide using a Claus plant and to the reduction of CO emissions.
Sulphur components are selectively removed from industrial gases at elevated pressures (20 to 60 bar) using physically acting absorbents such as Rectisol, Selexol, Genosorb, Morphysorb, with due consideration for the potential presence of CO2. Apart from the gas stream cleaned, the regeneration process also produces two regeneration gas streams at low pressure (1 to 3 bars) which contain the sour gas components removed: one stream laden with hydrogen sulphide and originating from a thermal regeneration column, one stream (or several streams) laden with carbon dioxide but almost free of hydrogen sulphide traces and originating from a non-thermal regeneration column, the carrier gas regeneration being effected, for instance, with the aid of nitrogen, and a further stream, if any, that is laden with carbon dioxide and originates from a flash column, without input of regeneration energy or regeneration carrier gas.
The stream laden with hydrogen sulphide is fed to the plant for the production of elemental sulphur by way of catalytic reaction in accordance with the Claus process. Apart from the elemental sulphur, this process yields a tail gas at almost atmospheric pressure (0.9 to 1.5 bar) that contains non-reacted sulphur components, such as hydrogen sulphide and sulphur dioxide, and hydrogen, carbon dioxide, carbon monoxide and nitrogen. In order to realise higher sulphur conversion rates (approx. >95%), the tail gas obtained in the Claus process is desulphurised by various methods in downstream units until the specified conversion rate is achieved, then subjected to a post-combustion and finally released into the atmosphere.
As an option, in accordance with the present state of technology, the tail gas obtained in the Claus process can first be fed to a catalytic hydration unit in which primarily sulphur dioxide as well as non-reduced sulphur components are converted to hydrogen sulphide, the said components being subsequently subjected to compression and recycled to the desulphurised main stream flowing to the absorption column at an elevated pressure of 20 to 60 bars or to the regeneration unit at a slightly higher pressure of about 1 to 3 bars. This recycling method of sulphur components not converted in the Claus process permits an almost 100-percent sulphur conversion of the sulphur components separated from the main gas stream.
The first disadvantage to be considered is the compression energy required for the tail gases, which is related to the high investment costs for compressors in order to cope with the rise in quasi atmospheric pressure to the 20-60 bar pressure of the main stream and specifically, the rise in pressure in the case of tail gas streams of small volumes and the choice of the adequate compressor type which must meet any operational requirement, for instance, that of existing traces of elemental sulphur.
In the second case, the disadvantage lies with the fact that the regeneration gas coming from the non-thermal regeneration column has a concentration that does not permit a non-polluting release of this stream into the atmosphere.
Hence, the objective of the invention is to improve the process in such a manner that on the one hand, the release of polluting off-gases into the atmosphere is avoided and on the other hand, a compression of the tail gas up to the pressure of the main gas stream is no longer required.